﻿////////////////////////////////////////////////////////////
// base64.h

// 参考文章：http://www.cstc.net.cn/docs/docs.php?id=202

//************************************************************************/
//    base64编码表
// 
//        0 A 17 R 34 i 51 z 
//        1 B 18 S 35 j 52 0 
//        2 C 19 T 36 k 53 1 
//        3 D 20 U 37 l 54 2 
//        4 E 21 V 38 m 55 3 
//        5 F 22 W 39 n 56 4 
//        6 G 23 X 40 o 57 5 
//        7 H 24 Y 41 p 58 6 
//        8 I 25 Z 42 q 59 7 
//        9 J 26 a 43 r 60 8 
//        10 K 27 b 44 s 61 9 
//        11 L 28 c 45 t 62 + 
//        12 M 29 d 46 u 63 / 
//        13 N 30 e 47 v (pad) = 
//        14 O 31 f 48 w 
//        15 P 32 g 49 x 
//        16 Q 33 h 50 y 
//
// base64编码步骤：
// 
//        原文：
//
//        你好
//        C4 E3 BA C3
//        11000100 11100011 10111010 11000011
//        00110001 00001110 00001110 00111010
//        49       14                            （十进制）
//        x        O        O        6        字符
//        01111000 01001111 01001111 00110110
//        78                                    （十六进制）
//        xOO6
//
//        解码：
//        xOO6
//        78 4f 4f 36
//        01111000 01001111 01001111 00110110
//        49       14 
//        00110001 00001110 00001110 00111010   31 0e 0e 3a
//
//        11000100 11100011 10111010
//        C4       E3       BA
//

#ifndef _BASE64_INCLUDE__H__
#define _BASE64_INCLUDE__H__

// 编码后的长度一般比原文多占1/3的存储空间，请保证base64code有足够的空间
inline int Base64Encode(char * base64code, const char * src, int src_len = 0); 
inline int Base64Decode(char * buf, const char * base64code, int src_len = 0);

__inline char GetB64Char(int index)
{
    const char szBase64Table[] = "ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz0123456789+/";
    if (index >= 0 && index < 64)
        return szBase64Table[index];
    
    return '=';
}

// 从双字中取单字节
#define B0(a) (a & 0xFF)
#define B1(a) (a >> 8 & 0xFF)
#define B2(a) (a >> 16 & 0xFF)
#define B3(a) (a >> 24 & 0xFF)

// 编码后的长度一般比原文多占1/3的存储空间，请保证base64code有足够的空间
inline int Base64Encode(char * base64code, const char * src, int src_len) 
{   
    if (src_len == 0)
        src_len = strlen(src);
    
    int len = 0;
    unsigned char* psrc = (unsigned char*)src;
    char * p64 = base64code;
    for (int i = 0; i < src_len - 3; i += 3)
    {
        unsigned long ulTmp = *(unsigned long*)psrc;
        register int b0 = GetB64Char((B0(ulTmp) >> 2) & 0x3F); 
        register int b1 = GetB64Char((B0(ulTmp) << 6 >> 2 | B1(ulTmp) >> 4) & 0x3F); 
        register int b2 = GetB64Char((B1(ulTmp) << 4 >> 2 | B2(ulTmp) >> 6) & 0x3F); 
        register int b3 = GetB64Char((B2(ulTmp) << 2 >> 2) & 0x3F); 
        *((unsigned long*)p64) = b0 | b1 << 8 | b2 << 16 | b3 << 24;
        len += 4;
        p64  += 4; 
        psrc += 3;
    }
    
    // 处理最后余下的不足3字节的饿数据
    if (i < src_len)
    {
        int rest = src_len - i;
        unsigned long ulTmp = 0;
        for (int j = 0; j < rest; ++j)
        {
            *(((unsigned char*)&ulTmp) + j) = *psrc++;
        }
        
        p64[0] = GetB64Char((B0(ulTmp) >> 2) & 0x3F); 
        p64[1] = GetB64Char((B0(ulTmp) << 6 >> 2 | B1(ulTmp) >> 4) & 0x3F); 
        p64[2] = rest > 1 ? GetB64Char((B1(ulTmp) << 4 >> 2 | B2(ulTmp) >> 6) & 0x3F) : '='; 
        p64[3] = rest > 2 ? GetB64Char((B2(ulTmp) << 2 >> 2) & 0x3F) : '='; 
        p64 += 4; 
        len += 4;
    }
    
    *p64 = '\0'; 
    
    return len;
}


__inline int GetB64Index(char ch)
{
    int index = -1;
    if (ch >= 'A' && ch <= 'Z')
    {
        index = ch - 'A';
    }
    else if (ch >= 'a' && ch <= 'z')
    {
        index = ch - 'a' + 26;
    }
    else if (ch >= '0' && ch <= '9')
    {
        index = ch - '0' + 52;
    }
    else if (ch == '+')
    {
        index = 62;
    }
    else if (ch == '/')
    {
        index = 63;
    }

    return index;
}

// 解码后的长度一般比原文少用占1/4的存储空间，请保证buf有足够的空间
inline int Base64Decode(char * buf, const char * base64code, int src_len) 
{   
    if (src_len == 0)
        src_len = strlen(base64code);

    int len = 0;
    unsigned char* psrc = (unsigned char*)base64code;
    char * pbuf = buf;
    for (int i = 0; i < src_len - 4; i += 4)
    {
        unsigned long ulTmp = *(unsigned long*)psrc;
        
        register int b0 = (GetB64Index((char)B0(ulTmp)) << 2 | GetB64Index((char)B1(ulTmp)) << 2 >> 6) & 0xFF;
        register int b1 = (GetB64Index((char)B1(ulTmp)) << 4 | GetB64Index((char)B2(ulTmp)) << 2 >> 4) & 0xFF;
        register int b2 = (GetB64Index((char)B2(ulTmp)) << 6 | GetB64Index((char)B3(ulTmp)) << 2 >> 2) & 0xFF;
        
        *((unsigned long*)pbuf) = b0 | b1 << 8 | b2 << 16;
        psrc  += 4; 
        pbuf += 3;
        len += 3;
    }

    // 处理最后余下的不足4字节的数据
    if (i < src_len)
    {
        int rest = src_len - i;
        unsigned long ulTmp = 0;
        for (int j = 0; j < rest; ++j)
        {
            *(((unsigned char*)&ulTmp) + j) = *psrc++;
        }
        
        register int b0 = (GetB64Index((char)B0(ulTmp)) << 2 | GetB64Index((char)B1(ulTmp)) << 2 >> 6) & 0xFF;
        *pbuf++ = b0;
        len  ++;

        if ('=' != B1(ulTmp) && '=' != B2(ulTmp))
        {
            register int b1 = (GetB64Index((char)B1(ulTmp)) << 4 | GetB64Index((char)B2(ulTmp)) << 2 >> 4) & 0xFF;
            *pbuf++ = b1;
            len  ++;
        }
        
        if ('=' != B2(ulTmp) && '=' != B3(ulTmp))
        {
            register int b2 = (GetB64Index((char)B2(ulTmp)) << 6 | GetB64Index((char)B3(ulTmp)) << 2 >> 2) & 0xFF;
            *pbuf++ = b2;
            len  ++;
        }

    }
        
    *pbuf = '\0'; 
    
    return len;
} 

#endif // #ifndef _BASE64_INCLUDE__H__